Relation between Nucleolus and Chromosomes. 63 
chromatin has no affinity reveal only the plastin portion of the nucleolus 
and as a much vacuolated structure. 
All the data at my command as a result of the study of the egg of 
Asterias forbesii support the view that the nucleolus is a storehouse of re- 
serve nutritive material, combining also the function of “ nuclein laboratory ” 
(Fick) in the sense that chemical alterations may transpire in the material 
while thus stored in the nucleolus. 
COMPARISON WITH HIPPONOE ESCULENTA. 
Material for a comparative study of the present problem in echinoderms 
was collected during a four weeks’ stay at the Marine Biological Laboratory 
of the Carnegie Institution of Washington at Dry Tortugas, Florida. It 
was my intention to extend the investigation over many different forms. 
Among at least ten different genera sufficiently abundant and apparently 
equally favorable for similar study, Hipponoé esculenta alone had ripe eggs 
at the time I left the island on June 13. From the appearance of the gonads 
at that time it seemed probable that most of these forms would not ripen 
their eggs for several months. 
Hipponoé esculenta was apparently at the height of its breeding season 
during May and the early part of June. Due to the smaller size of the egg, 
and particularly to the fact that the odcytes mature in the ovary, this form is 
much less favorable for a study of the maturation phenomena than Asterias, 
where the process takes place after spawning and can be readily observed 
and controlled in the free egg. Unsuccessful attempts were made to induce 
the immature odcyte of Hipponoé in sea-water to form the polar bodies by 
agitation, the addition of sperm, and the addition of various salts and acids. 
However, the addition of a drop of HCl to a dish of sea-water containing 
mature eggs caused a small percentage to develop through the early cleav- 
age stages. Controls of eggs from the same batch and in the same water 
without the HCl showed no segmentation stages. 
As in Asterias, there is in the ovary of Hipponoé a striking lack of tran- 
sition stages between the odgonia and the full-grown primary oocyte, giv- 
ing evidence of the great brevity of the growth-process. The infrequency of 
the odcytes in maturation shows that this process also is consummated very 
quickly. Batches of eggs taken from the ovary of even the smallest speci- 
men yielded at the highest only about 10 per cent of immature ova. In the 
larger specimens all the ova were fully matured. A section through the 
ovary of the latter revealed a layer of odgonial cells, a few immature full- 
grown oécytes, and a large number of mature ova. The female pronucleus. 
is comparatively larger than that of Asterias, and it is characteristically 
devoid of a nucleolus (fig.95). Toto mounts of eggs show two small polar 
bodies. Sections of the first polar body reveal an attempt at a second 
division (fig. 94). 
